Extended repayment plan with variable interest loans

Hello! I have had loans since 2004 so I have some variable interest ones. I am also on the Extended Repayment plan and have been since 2013. In that time, even with the interest steadily increasing on those variable interest loans, my servicer never changed my payment amount. While I was considering refinancing my loans, I asked them to provide me with something that would show how much interest I will pay over the rest of the term. In generating this information for me, I guess they realized that I would not pay the loan off by the end of the term because of this so they recalculated (increased) my payment, which is fine. However, the ratio of interest to principal has steadily been increasing on these loans and for the last over two years, not a single penny has gone to principal on any of the unsubsidized loans.

It is my understanding that my payment should have changed based on the increase/decrease of interest rates on those variable rate loans. Is this not the case?